Daylight fluorescent pigment compositions



Patented Feb. 21, 1950 DAYLIGHT FLUORESCENT PIGMENT COMPOSITIONS JosephL. Switzer, Cleveland Heights, and Robert C. Switzer, South Euclid, OhioNo Drawing. Application January 30, 1945, Serial No. 575,364

24 Claims. (01. 252-3012) This invention relates to an improvement inluminescent substances, and more particularly, to pigments, coatingcompositions, and coatings which exhibit the phenomenon termed daylightfluorescence. This application is a continuation-in-part of ourcopending applications, Serial No. 414,285, filed October 9, 1941,Serial No. 452,- 522, flled July 27, 1942, and Serial No. 455,610, filedAugust 21, 1942.

As pointed out in the above identified applications, the fluoragentsavailable to the prior art could be classified generally as inorganicfluorescent pigments or organic fluorescent dyes, the term fluorescentdyes as employed in this specification and the appended claims beingunderstood to include soluble fluorescent organic dyestuffs, fluorescentintermediates and like fluorescent organics, except unsubstitutedhydrocarbons.

Of the two classes of fluoragents, the inorganic pigments, such as theactivated metal sulphides, were most widely employed. Such inorganicpigments were far from satisfactory for use in coating compositions,being generally coarse and relatively unstable upon exposure toweathering conditions, as compared with good non-fluorescent pigments.Further, while such inorganic fluorescent pigments possess excellentfluorescent brightness on exposure to fluorescigenous radiations (suchas ultraviolet) in the substantial absence of visible light, the colorsof such inorganic fluorescent pigments in normal daylight are generallya dull off-shade white or weak pastel tints of green or yellow. [Theterm daylight as used in this specification and appended claims refersto sunlight, or other light having a spectrum con- :3.

ing compositions are generally used mainly as backgrounds in combinationwith ordinary subtractive coating compositions which supply the contrastand color necessary for daylight viewing. Recent research and synthesisof inorganic fluorescent pigments have improved them as to fineness andresistance to weathering, but efforts to improve their strength orpurity of daylight color have been comparatively fruitless and have beenpursued with little eventual enthusiasm, due to the apparent antithesisof strong subtractive color, on the one hand, and efficient fluorescenceon the other. The failures to obtain pigments having both a strongsubtractive color and eflicient fluorescence were often excused on theground that, on the one hand, the theory of fluorescence teaches thatthe visible light emitted by a fluorescing substance is the reemittedenergy of the light of a different color or wave-length which had beenabsorbed by the fiuorescing substance, whereas, on the other hand, thereflection-absorption theory of color teaches that the color of asubstance is due to a partial reflection of incident visible light, theunreflected portion of the incident visible light being absorbed anddissipated as heat. Thus, it was expected that the absorptive eifect ofa pigment having a relatively strong subtractive color would dissipateas heat the incident energy necessary to excite the pigment tofluorescence.

The foregoing conclusion was employed to explain an eiiect noted inconnection with fluorescent dyes. Weak solutions of many dyes known tothe prior art were often brilliantly fluorescent and somewhat moretinctorial than inorganic pigments of equal fluorescent brightness.Unfortunately, the notorious fugitiveness, upon exposure to daylight, ofsuch weak concentrations of fluorescent dyes was one of the principalreasons which discouraged their practical use as fluoragents to be usedin visible light. Efforts to stabilize such fugitive dyes by usualprocedures. i. e., by increasing their concentration or by formingstable metal salts or lakes, either greatly diminished or destroyedtheir fluorescence. The above conclusion, namely, that a strongsubtractive color destroys or diminishes the possibility offluorescence, still appears to be a valid explanation for the loss ordestruction of fluorescence when the above expedients are employed tostabilize dyes which are fluorescent in weak concentrations. As pointedout in our prior application, Serial No. 414,285, we have demonstratedthe probable invalidity of another theory which is still often advanced,namely, that fluorescence of organic materials, such as dyes, is aphenomenon associated with the photochemical decomposition of the dyes,similar to the luminescence noted in connection with certain chemicalreactions and termed chemi-luminescence, and thus, if such dyes wererendered light-fast, by increasing their concentration or by formingstable metal lakes, then, according to the theory, fluorescence of thedyes would be prevented because photochemical decomposition of the dyeswould be prevented.

It is an object of this invention to provide pigments, coatingcompositions, and coatings [said compositions and coatings embodyingsaid pigments] which are not only brilliantly fluorescent when exposedto fiuorescigenous radiations in the substantial absence of visiblelight but which are also so bright in color, under daylight, that, inapplications where effective purity and brightness of color in daylightis the prime requisite, they are vastly superior to the subtractivecolored pigments, coating compositions, and coatings of the prior art.

It is an advantage and startling result of our invention that a coatingemploying our pigments may project more light'of a given color than ispresent in the visible light incident to such coat ing; for thisphenomenon we have coined the term daylight fluorescence in the absenceof nomenclature in the prior art. This phenomenon is most strikinglyobserved in colors which are predominantly of the longer wave-lengths ofvisible light; for example, red coatings employing our pigments mayproject as much as 120 to 130% of the light of a corresponding color inthe incidentvisible light. Due to this phenomenon of daylightfluorescence, the colors of our composition are extremely bright and farexceed normal subtractive colors in distinguishability at a distance;due to the fact that our daylight fluorescent compositions can project adisproportionately large amount of light of the dominant waveband, thecolors may be exceedingly pure in their total effect. The surprisingbrightness of coatings containing our pigments may be appreciated whenit is realized that a subtractive-colored pigment of the prior arthaving the samepronortional purity and which reflected as much as 60% ofthe incident visible light in the dominant waveband was heretoforeregarded as exhibiting an exceedingly bright and pure color.

So far, and without restricting ourselves to subsequently developedtheories, we account for the phenomenon of daylight fluorescence on thetheory that, whereas the known subtractive-colored compositions of theprior art exhibited color by virtue of the well-recognized phenomenon ofre fleeting a greater portion of a wave-band or wavebands in theincident visible light than the other wave-bands in such light andabsorbing and dissipating the balance of such light, our compositionsexhibit color not only by reflecting a dominant wave-band of theincident visible light but also by emitting a portion of the remainingenergy of the incident light as light of the dominant wave-band. To theeye, of course, the reflected light and emitted light is all light ofthe dominant wave band. Fluorescigenous energy which is converted tofluorescent light is. in many instances, not only invisible untravioletbut also visible light of shorter wave-lengths than the light of thedominant wave-band.

It is a further object of this invention to pro vide pigments, coatingcompositions, and coatings which are daylight fluorescent and which aresufliciently stable in daylight and under weathering conditions topermit their use in many practical applications. It is an advantage ofour invention that our compositions may be produced in a wide range ofcolors varying, for example, from blue to red.

Other objects and advantages of our invention will be apparent from thefollowing description of specific examples of our invention and from theappended claims.

In general, we have discovered that we may obtain daylight fluorescentcoating compositions and coatings by utilizing as a combined fiuoragentand chromogenic agent an organic dye which exhibits color when insolution and which fluoresces in response to long wave or nearultraviolet when in a weak solution in a transparent solvent, providedthat two further conditions are met:

(a) The concentration of the dye in the solvent must be sufliciently lowto prevent substantial dissipation of incident fluorescigenous energy asheat by the dye molecules themselves, and

(b) the depth of the solution (with respect to the direction of theincident daylight) must be sufficient to permit the dye to convert andmodify an appreciable percentage of the incident daylight transmitted bythe transparent solvent for the dye and the transparent vehicle in whichthe solvent for the dye is dispersed.

The above further conditions were derived from observing that thetinctorial effect of a weak solution of a fluorescent dye could bematched by a still weaker solution of the dye if the depths of 'the twodye solutions were substantially inversely proportional to theconcentrations of the dye in the solutions. It was then discovered thatthe tinctorial strength of strong, substantially nonfluorescentconcentrations of a dye could be equaled by weak fluorescentconcentrations of the dye provided that the depths of the two solutionswere, again, substantially inversely proportional and thelight-diffusing property of the less concentrated (and, consequently,more transparent) solution was properly augmented, as by means of aproper diffusely reflecting background, for example. In short, (b),above, signifies that tinctorial strength is a'function of the number ofmolecules of dye per unit of area of surface covered by the dye. Thus,to obtain both fluorescence and tinctorial strength we (a) limit theconcentration of dye to obtain fluorescence and (b) vary the depth ofthe solution per unit of area of surface covered to obtain the desiredtinctorial strength. This last step is in contradistinction to the priorart, which increased tinctorial strength by increasing the concentrationof dye. Our limitations are conveniently expressed in terms of (a) gramsof pure dye per cubic centimeter of coating and (1)) grams of pure dyeper square centimeter of surface covered by the coating.

It should be noted that in the foregoing general description of the typeof limitations necessary for daylight fluorescence, the dye is describedas being in solution, for we have noted that the dyes must be insolution or, if present in a solid, be in a state akin to solution, 1;e., the dyes must be solvated. It is also to be noted that the dyes,when limited in terms of grams per unit of measure, are described aspure dyes; many commercial dyes are supplied in a relatively impurestate or are diluted or extended. The relative purity of the actual dyeemployed must be taken into account in compounding daylight fluorescentpigments and coatings within the following limits.

aacaaoa As pointed out in our above identified application, Serial No.455,610, a peculiarity of daylight fluorescent dyes is that thepermissible concentration of dyes decreases as the wave-length of thepredominant wave-length of light projected by the solvated dyeincreases. Likewise, it has been found that the permissible volume ofdye per square centimeter of surface being covered decreases as thewave-length of the dominant wavelength of light projected by thesolvated dye increases. Thus, for example, the permissible max imumnumber of molecules of solvated dye per square centimeter of surfacecovered is less for red daylight fluorescent dyes than for orangedaylight fluorescent dyes, less for daylight fluorescent orangedyes'than for yellow dyes, and so forth through the spectral colors. Apeculiar convenience of expression arises when the dye is specified byweight rather than by number of molecules, because, in general, themolecular weight of dyes capable of exhibiting daylight fluorescenceincreases as the dominant wavelength of projected light increases inwave-length, thus tending to counterbalance the above stated decrease inpermissible volume of dye per unit of area, so that in our daylightfluorescent compositions:

.0005 gram of dye per square centimeter of coating is a practicalmaximum in any daylight fluorescent system composed of a single dye anda solvating material.

000% to .00003 gram of daylight fluorescing dye per square centimeter ofsurface covered [and at concentrations of less than .01 gram per cubiccentimeter of coating] will produce optimum daylight fluorescence.

.000015 gram of daylight fluorescing dye per square centimeter is theminimum amount of dye which will exhibit daylight fluorescence of highchroma or purity of color, although for purposes of tints, no practicalminimum has been found, since daylight fluorescent tinting effects havebeen noted in dilutions exceeding one part of daylight fluorescing dyein many million parts of solvating material.

The effect of the wave-length of the dominant wave-length of lightprojected is more apparent in connection with the permissible maximumconcentration of dye in the solvating material. Thus:

.015 gram per cubic centimeter of solvating material in the finalcoating is the permissible maximum for red daylight fluorescing dyes.

.025 gram per cubic centimeter of solvating material in t e finalcoating is the permissible maximum for yellow green dyes.

as is the provision of a solvating material and/ or vehicle which doesnot absorb appreciable amounts of incident daylight or projected light.Thus dark, turbid, solvating materials are to be avoided; waterwhitesolvating materials applied upon a white difiusing background aregenerally best, though milky-white solvating materials are oftenexcellent where the ingredient causing milkiness is a difiuser ratherthan an absorber.

It is to be noted further that the foregoing maxima. and minima arestated for a single dye in a solvating material. It is often desirableto use a plurality of daylight fluorescing dyes in the same solvatingmaterial. In such cases, and where the predominant emission wave-bandsof the dyes do not overlap, as in the case of the red dyes andyellow-green dyes, it is possible to use concentrations of each up toits permissible maxima.

When, to obtain maximum intensity of color, it is necessary to use themaximum grams of dye per square centimeter, it is preferable to use thelower values of dye per cubic centimeter of solvating material in thefinal coating, that is, in short, to use thick Coatings in which the dyeconcentration is very low.

In order to obtain coatings which exhibit the desired daylightfluorescence, it is possible to dissolve the dye in a suitablefilm-forming vehicle. We prefer to obtain the desired coatings havingthe necessary a ounts and concentrations of daylight fluorescing dyes bypigmented coating compositions. That is, the dyes are dispersed in asuitable, substantially solid, solvating material which will maintainthe dyes in a solvated state. The dyed solvating material is then groundto fine pigment size and dispersed in a vehicle, which may include avolatile vehicle solvent, to form a coating composition. The advantagesof daylight fluorescent pigmented coating compositions are: First, itpermits a wider variety of vehicles to be used and thus provides a widerscope of application while affording the fluorescent stability of hardbut fragile thermo-set coatings. Second, better control of dyeconcentration is obtained; if the dye is merely dissolved in the coatingcomposition vehicle, fluorescence-quenching skinning effects may beobtained due to migration and excessive concentration of dye at thesurface of the coating during volatilization of solvents in the coatingcomposition. By having the dye dissolved in the pigment rather than inthe vehicle, skinning of the coating, no matter how bad, cannotconcentrate the dye in excess of a maximum concentration fixed by theconcentration of the dye in the pigment.

We have discovered that the proper solvating materials for daylightfluorescing dyes are polymerizable thermo-setting resinous materials inwhich the dyes will be held in a solvated state when the materials arepolymerized. The advantages of such materials are many-fold. Althoughsuch thermo-setting resinous materials may vary from tough, horn-like tobrittle glass-like materials when polymerized, the fact that suchpolymerized materials are thermo-setting, rather than thermo-plastic,permits them to be ground to minute pigment-size particles whereasparticles of the common thermoplastic material will tend to cohere andgum up during grinding. Other excellent pigment characteristics of suchmaterials are that the finely ground powders may be readily dispersed inmost coating composition vchicles Without flocking and withoutdissolving; further, such pigments are usually remarkably inert bothwith respect to the vehicle and the solvated dye, impervious and stable.Being essentially amorphous, such pigment materials tend to hold thesolvated dyes in a homogeneous dispersion throughout a pigment particle,thus enveloping and protecting relatively unstable dyes, rather thantending to throw the dyes out of solution onto the surface of a pigmentparticle, as in the case of crystalline materials. As pointed out in ourapplication, Serial No. 452,522, unplasticized, unmodifiedurea-formaldehyde or alcohol-modified urea-formaldehyde resins exert amarked stabilizing effect upon'the fluorescent life of daylightfluorescent dyes; these materials are, therefore, generally preferred ascarriers for the dyes in our pigments, not only because of the desirablepigment properties of the general class of thermo-setting resins butalso because of their remarkable stabilizing effect upon the solvated des.

To solvate the dyes in the suitable pigment carrier, one of thefollowing procedures may be employed:

' (a) The dye is dissolved in a solution of the unpolymerized resin anda mutual solvent for the resin and dye so that concentration of dye inthe resin will not finally exceed the applicable maximum. The resin isthen polymerized by heat,

alone, or by heat in the presence of a catalytic agent, such as an acid.The polymerizedresin is then ground to fine pigment size, preferablyuntil the average size of resin particles ranges between .2 to 2.5microns, although the size may be larger for use in certain coatingcompositions which will tolerate coarser pigments, such as, for example,screening lacquers. The dyed resin may be ground dry, or wet, or even inthe coating composition vehicle, although dry grinding is generallypracticed to permit the pigment particles to be air-classified so thatlarger particles may be returned to the millfor further grinding. Theoperativeness of this procedure depends, of course, upon the ability ofthe dye to withstand the often rigorous conditions of polymerization andgrinding and the ability of the resin to hold the dye in a solvatedcondition.

(b) The undyed resin is polymerized and ground, similarly to the dyedresins above. The dye is dissolved to provide a dye bath in which theconcentration of dye may, though not necessarily, exceed theconcentration maxima given above. The ground polymerized resin is thendispersed in the dye bath and dyed by the migration of dye from solutionin the dye bath to a solvated condition in the resin pigment powder,care being exercised so that the concentration of dye in the pigmentparticle solvent does not exceed the permissible maxima. The dyed resinpigment particles are then removed from the dye bath and are generallyWashed and dried, although the washed wet filter cake of pigment may beflushed directly into the coating composition vehicle where the vehiclewill preferentially wet the pig mcnt particles. The operativeness ofthis procedure depends, of course, upon the ability of the poylmerizedor hardened resin to solvate the dye. Although unplasticized, unmodifiedurea-formaldehyde and unplasticized, alcohol-modified ureaformaldehyde,for example, are dense, hard, substantially impervious glass-likematerials which show no practical substantivity for the dyes when theresins are polymerized in sheets and bars, nevertheless, it has beenfound that pigment powders of these materials possess the power oftaking up most daylight fluorescent dyes from a dye bath solution. Theprobable explanation for this phenomenon is that, in so far as the dyein the dye bath is concerned, the resin pigment particles are merelyparticles of a super-cooled liquid having great solvating power for thedye, the hardness of the particles merely slowing the rate of dyedispersion into the particles, and, because the particles aresubstantially all surface, the slightest depth of penetration of thepigment particles by the dye will be substantially complete penetrationand, thus, the low maximum permissible dyeresin concentration may bereached relatively quickly.

0! the foregoing procedures, the first (a) has the advantage ofpermitting accurate control of the dye-solvating resin ratio and is,accordingly, recommended when pigments having dye-resin concentrationsapproaching the permissible maxima are desired. The second (b) has theadvantage of permitting the use of dyes which are adversely affected bythe conditions of polymerization and also provides a convenientprocedure for manufacturing when it is desired to produce small batchesof pigments 'of different colors. It is also to be understood that theabove procedures are not limited (a) to the use of completelyunpolymerized resins nor (b) to th use of completely polymerized resins;depending upon the degree of polymerization, partly polymerized resinsmay be dyed either before or after grinding and before completepolymerization. It may even be an advantage to postpone completepolymerization where the pigments are to be used in baking lacquers,molding compositions, or as molding powders per se, to permitpolymerization to be completed by the heat employed in subsequent bakingor molding operations.

Selection of coating composition vehicle Dry pigments made according toour foregoing procedures usually give no indication whatsoever of thedaylight brilliance which they impart to the ultimate coatings. Instead,the dullish, chalky, pastel appearances of the finely ground pigmentpowders would seem to indicate that these organic fluorescent pigmentsare similar to many inorganic fluorescent and phosphorescent pigments inthat grinding to small pigment size reduces or destroys fluorescence,for our coarser pigments, though still chalky and dull, are lessstrikingly so. We have discovered, however, that the chalky pastelappearance of our dry pigments is due to the extreme effect of the indexof refraction of the solvating carrier for the dye with respect to theair which wets the dry pigment particles and that such chalkiness may becured by dispersing and wetting the pigments in a coating compositionvehicle which has substantially the same refractive index as the carrierof the pigment in which the dye is solvated.

The importance, if optimum results are to be obtained, of selecting acoating composition vehicle having substantially the same refractiveindex as the refractive index of the solvating dye carrier of ourpigment is apparently due to the fact that our pigments owe their colornot only to reflected incident light but also to incidentfluorescigenous light. Thus, any total reflection due to a difference inthe refractive indices of our pigment and its vehicle robs the pigmentnot only of light which may be reflected but also of fluorescigenouslight. Minimum total reflection is obtained. of course, when the indicesof refraction of the pigment and vehicle are equal, and it has beenobserved that no appreciable chalkiness is apparent if the difference inindices of refraction of the pigment and vehicle is less thanapproximately fifteen per cent of either one; if the difference inindices of refraction is increased more than this extent, the coatingcomposition tends to become chalky.

For optimum brightness, the coating composition vehicle is preferablytransparent, not only to visible light but also to near ultraviolet. For

optimum fluorescent stability, the coating com- Preparation of coatingcompositions and coatings As pointed out above, the maximumconcentration of solvated dye in the ultimate coating composition islimited' by the concentration of solvated dye in the pigment. However,in the ultimate coating, the transparent coating composition vehiclesolids are, in a sense, as much of a diluent for the solvated dye as thesolvating carrier for the dye in the pigment and must, therefore, betaken into account in the computation of the weight of dye per unit ofarea and per unit of volume in the ultimate coating. If the ultimatecoating, as in a printed or painted area or in a coated fabric or thelike, is limited to a maximum permissible thickness, care must beexercised in formulating the coating composition so that the proportionof coating composition vehicle solids is not so great that the minimumamount of dye per unit of area necessary for high chroma or purity ofcolor cannot be obtained in the ultimate coating.

When a coating composition is prepared by dispersing our daylightfluorescent pigments in a transparent vehicle, the composition may be sodark in color (particularly when viewed in a can or other relativelydeep vessel) as to give no indication of the extreme brightness andpurity of color which may be obtained in the ultimate coating. If so,such darkness will be primarily due to'the fact that the depth of thecoating is such that the amount of dye per unit of surface area exceedsthe permissible maximum; the light reflectance factor of the interior ofthe vessel will also aflect the brightness of the coating composition.It is in such relatively great depths that the effect of differences intransparency of the vehicles and solvating carriers, which may be neligible in the coatings, become pronounced.

For a given coating having a dye concentration within the limits setforth above, the whiteness of the surface on which the coating isapplied is a major factor affecting the brightness of the coating. Thus,optimum results are obtained on white surfaces having a reflectancefactor (based upon comparison with a standard magnesia block) of eightyper cent or better. If it is not convenient or permissible to employ awhite background, the next best background is one having a brightsubtractive color similar to that of the dominant wave-band of thecoating. Such subtractive-colored backgrounds are generally lessdesirable than. white backgrounds because they are generally lesseflicient reflectors of the dominant waveband and often absorb incidentfluorescigenous light. The coating may, of course, be relativelyindependent of its background if the coating contains a suspension ofdifiusely reflecting particles or bodies, or if the surface to which thecoating is applied is roughened and the index of refraction between thecoating and its supporting surface is such that diffuse total reflectionis obtained in that interface; in such instances, the coating, ineffect, carries its own diffusely refiecting background.

Generally, our coating compositions comprise 10 a daylight fluorescentpigment dispersed iii a liquid vehicle to permit the coatings to beapplied to a suitable receiving surface as inks, paints,lacquer-enamels, fabric coating and impregnating compounds which may beappliedby customary suitable equipment and procedures, as by brushing,printing, screening, spraying, dipping, roll-coating, knife-coating, andthe like. The coatings may cover the entire surface area of thesupporting surface or only delineated portions thereof.

Specific illustrative but not limitative examples of daylight.fluorescent pigments made according to our invention are as follows:

Example 1 Parts (by weight) (1) Butyl alcohol-modified urea-formaldehydesolution (50% solids) 50 (2) 4 amino 1,8 naphthal p-xenylimide .2

The daylight fluorescent dyestuif (2) is dissolved in the resin solution(1) and the dyed resin solution is then polymerized by a suitableprocedure, as by heating at C. until jelled, cutting the jell into smallpieces and curing at 140-145" C. until the dye-d resin is polymerized toa glasslike hardness. (Such curing should be conducted under wellventilated conditions, e. g., in an air circulating oven.) The dyedpolymerized resin is then ground until the particles will pass a 200-mesh screen, as by first grinding the material in a hammer mill and thengrinding in a pebble mill and passing through an air-classifier whichwill remove the fines of the desired pigment-particle size and returnthe coarser particles to the mill for further grinding.

The dye in the pigment made according to this example will be solvatedin the polymerized resin carrier at the ratio of .01 grams of dye percubic centimeter of carrier. When dispersed in a suitable vehicle andapplied in a coating of proper thickness on a white surface, thispigment will exhibit brilliant yellow-green fluorescence.

Example 2 I Parts (by weight) (1) Aqueous dispersion of unmodifiedurea-formaldehyde resin (50% solids (2) 4 amino 1,8 naphthalp-xenylimide .417 (3) Ethyl ester of meta monoethylaminophenol-phthalein hydrochloride .0625

The dyes (2 and 3) are dissolved in the resin dispersion (l), which isthen polymerized and ground by suitable means and procedures, as inExample 1. In the resultant pigment the weight of dye (2) projectingyellow-green light is .0104 gram and of dye (3) projecting red-orangelight is.00156 gram per cubic centimeter of solvating resin. theprojected light of the two dyes being additive to project a brilliantrich yellow daylight fluorescence when properly dispersed and applied ina coating.

Ezcample 3 Parts (by weight) (1) Butyl alcohol-modified resin solutionThe dyes (2, 3, and 4) are dissolved in the resin solution (1) which isthen polymerized and ground by suitable means and procedures, as inExample 1. Inthe resultant pigment the weight Example 4 Parts (byweight) (1) Alcohol solution of alcohol-modified urea-formaldehyde resin(50% solids) 100 (2) Methyl alcohol 200 (3) Ethyl ester of metamonoethylaminophenolphthalein hydrochloride 1 der is then filtered fromthe solution, washed and dried. When suitably dispersed and applied in acoating, the pigment exhibits a bright pinkishsalmon daylightfluorescence.

Example 5 Parts (by weight) (1) Succinic anhydridenu 100 (2).Pentaerythritol -68, (3) Ethylene glycol monomethyl ether 5' (4) Metadiethylaminophenol-phthalein hydrochloride .5

The succinic anhydride and pentaerythritol are mixed and heated in abeaker on a hot plate until the liquid which forms indicates the startof polymerization by becoming viscous. The dye (4) is diisolved in thesolvent (3) and the dye solution is added to the resinous carrier (1 and2). The mixture is then further heated with stirring to thoroughlysolvate the dye in the resinous mass and evaporate the dye solvent (3)from the mass. When the mass has become extremely viscous, it is pouredinto shallow pans and cured at 135-140 C. until very hard. The dyedpolymerized mass is then broken out and ground to proper pigment size.The resulting pigment has a dye concentration of approximately .005 gramof dye per cubic centimeter of polymerized thermo-set solvatingmaterial. When properly dispersed and applied in a coating, the pigmentexhibits an extremely brilliant, rich red daylight fluorescence.

It is to be understood that other polymerized thermosetting resinousmaterials may be employed for the solvating dye carrier in a like mannerto those disclosed in the foregoing examples. Such other materials whichhave been found suitable for the purposes of this invention include, forexample, casein-modified urea-formaldehyde resins, melamine resins,silicone resins (methylated from 1 to 1.9 methyls/siiicon) methylsilicols'copolymerized with alcohol-modified urea-formaldehyde, and thelike. Still other like and probably better dye solvating carrier mate'-rials will undoubtedly be discovered in the future.

An example oi. a coating composition and coat-v ings made according toour invention is as follows:

Example 6 Parts (by weight) (1) Solution ormethyl methacrylate (40%solids) -i 100 (2) Pigment (according to Example 5) The above pigment(2) is thoroughly dispersed in the coating composition vehicle (1) toprovide a coating composition which is suitable as a screeninglacquer-enamel. In this coating composition the weight of the dye pervolume of carrier and vehicle solids will be approximately .0028 gram ofdye per cubic centimeter of coating solids. Thus, to provide a coatinghaving optimum fdaylight fluorescent brightness, the lacquer printedwith m mi n The;,.-permutat i h' h can be made according to should bescreened upon the coated surface to provide an ultimate coatingapproximately 6 mils thick; in such thickness the solvated dye will bedispersed at the rate of approximately .000042 gram per squarecentimeter of surface.

By screening the above lacquer in the thickness given and in largedelineated areas upon good white paper and in juxtaposition to largeareas printed in asubtractive red, which would normally be considered abright, rich red, to provide a billboard poster, the extreme brightnessof the areas printed with our daylight fluorescent coatirig will makethe areas printed with conventional bright subtractive red inks seemdark and dull by contrast,when the billboard is viewed in daylight. Atdistances of about one hundredfeet or more, the contrast is so greatthat the areas pigments actually seem to be nt source of artificialilluau m ntedb I r u -and combinations of the m n i umerous suitablecoating v ilable are such that subes ed; coating composition and latedto meet any particuy'those skilled in the art, the requirement for thenecessary depth of coating to provide the required weight of dye perunit of area in the ultimate coating excluding, of course, the use ofour pigments in ultimate coatings which must be very'thin.

Suitable transparent coating composition vehicles which have been foundsuitable for particular pigments disclosed in Examples 1 to 5, above,include, in addition to the methyl methacrylate given in Example 6,butyl methacrylate, nitrocellulose, nitrocellulose modified bymethacrylate resins or by drying or non-drying oil-modified alkydresins, simple alkyd resins, such as those derived from sebacic acid,urea-formaldehyde suitably modified for use in baking lacquers, and thelike. Other suitable vehicles for our pigments will be known to thoseskilled in the art. As an example of a vehicle which will not afford theoptimum utilization of the daylight fluorescence of our pigments, due toan excessive difference in the indice's of refraction of the carrier andvehicle, if anorangepigment, as disclosed in Example? is 'dispers'edina. f fteen per cent aqueous solutionfof agvehiclecomprised of ammoniumcaseinate and this coating composition is allowed to dry, then theresulting coating, when viewed in daylight, will be a chalky, pastelpinkish-orange, rather than the rich, brilliant orange obtained when thesame pigment is dispersed in a transparent vehicle having a refractiveindex more closely approximating that of the pigment carrier.

It is to be understood that our coatings are not necessarily dependentupon a diffusely reflecting supporting surface for optimum daylightfluores cent effects. Thus, if our pigment is dispersed ina vehiclewhich is, in itself, comprised of two or morev transparent mediumshaving sufficient differences in refractive indices to provide a diffuserefiection within the vehicle but not with respect to the dispersedlight-modifying pigment, the desired diffuse reflection may be obtained.For example, if forty parts of dinaphthoxy ethane powder is mixed withfifty parts of nitrocellulose dissolved in ethyl acetate and fifty partsof a non-drying oil modified alkyd resin in a toluene solution, such amixture, when dry, will provide a suitable self-diffusing vehicle forour pigments having an alcohol-modified urea-formaldehyde pigmentcarrier. Likewise, when our coating is preformed as a cast film, onesurface of the film may be etched or abraded to provide a diffuselyreflecting surface.

From the foregoing specific examples, it should be apparent that furthermodifications and variations may be made by those skilled in the artwithout departing from the scope of our invention as defined in thefollowing claims. In the following claims, it is to be understood thatthe term transparent as applied to the solvating dye carrier and thecoating composition vehicle means that the carrier and vehicle are notopaque to either the light projected by the solvated dye or thefluorescigenous light which excites the dye to fluorescence. The termindex of refraction refers to the index of refraction relative to air.It is also to be understood that the term dye refers to pure dye; thatwhen a dye is said to project light of a given color, such color is thedominant wave-band of light projected by the dye; and that the termdilute solution means a solution of dye having a concentration of dyenot greater than the concentration of dye stated in the claim. It is tobe further understood that the term polymerized carrier means thermosetting resinous material polymerized to the extent that the material maybe crumbled under shearing loads.

What is claimed is:

1. An article comprising a structure having a daylight fluorescentsurface area, said area comprised of a layer comprising a dye exhibitingdaylight fluorescence when said dye is in dilute solution, solidparticles of a transparent polymerizcd thermo-set resin carrier for saiddye dispersed in said layer, said carrier maintaining said dye in asolvated state and said dye retaining its daylight fluorescence whensolvated in said carrier, the maximum weight of said dye per volume ofcarrier varying from substantially .025 gram for dyes projectingyellow-green light to substantially .015 gram of dye per cubiccentimeter of solvating carrier for dyes projecting red light and theweight of dye per square centimeter of surface of the article notexceeding .0005 gram of dye for each spectral wave-band of lightprojected and a transparent resinous vehicle'binding said carrierparticles together. 7

2. A daylight fluorescent article as defined in claim 1 in which saidlayer has a relatively smooth outer surface and an opposite relativelyroughened surface to diffuse light entering said coating through saidsmooth surface.

3. An article comprising a structure having a daylight fluorescentsurface area, said area comtion vehicle in which said particles aredispersed,

the weight of said dye per square centimeter of surface covered notexceeding substantially .0005 gram of dye per square centimeter, and adiffusely reflecting surface covered by said coating.

4. An article having a daylight fluorescent surface coating comprising asolvated dye exhibiting daylight fluorescence when in-dilute solution,solid particles of a transparent thermo-set resin carrier having thepower to dissolve said dye when said resin is in a liquid state and saiddye being dispersed in said carrier in a solvated state and said dyeretaining its daylight fluorescence when solvated in said carrier, themaximum proportion of said dye to said carrier varying fromsubstantially .025 gram for dyes projecting yellowgreen light to .015gram for dyes projecting red light per cubic centimeter of solvatingcarrier. a transparent film of a resinous coating composition vehicle,the maximum difference in indices of refraction of said carrier and saidvehicle not exceeding substantially fifteen per cent of the greaterindex of refraction, said particles of carrier being dispersed in saidvehicle, a surface diffusely reflecting light projected by said dye andcovered by said coating, the thickness of said coating beingproportioned with respect to the amount of dye solvated therein so thatthe weight of dye per square centimeter of area covered does not exceed.0005 gram.

5. An article as defined in claim 4 in which the amount of dye persquare centimeter of surface covered is at least .000015 gram.

6. An article as defined in claim 4 in which the proportion of dye tocarrier is less than .01 gram of dye per cubic centimeter of coating andthe amount of dye per square centimeter of surface covered variesbetween .00006 and .00003 gram.

7. An article comprising a structure having a daylight fluorescentsurface area, said area comprising a layer of coating comprising a dyeexhibiting daylight fluorescence when in dilute solution, solidparticles of a thermo-set transparent resin in which said dye issolvated and said dye retains its daylight fluorescence when solvated insaid resin, the maximum proportion of dye to resin being substantially.01 gram of dye per cubic centimeter of resin, a transparent coatingcomposition vehicle in which said resin particles, carrying saidsolvated dye, are dispersed as a pigment, the maximum difference in theindices of refraction of said resin and vehicle being substantiallyfifteen per cent of the larger index, and a white surface supportingsaid coat ng, said coatingbeing of a thickness to provide between.000015 and .00006 gram of solvated dye per square centimeter of surfacecovered by the coating.

8. An article comprising a structure having a daylight fluorescentsurface area, said area comprising a layer of coating comprising a dyeexhibiting daylight fluorescence when in dilute solution, solid pigmentparticles comprised of a solvating polymerized thermo-set resin carrier15 for said dye, said dye being solvated in said projecting yellow-greenlight to a maximum .of

substantially .015 gram for dyes projecting red light per cubiccentimeter of carrier and said dye retaining its daylight fluorescencewhen solvated in said carrier, a transparent vehicle in which said dyedpigment particles are dispersed, a transparent medium in said vehiclehaving an index of refraction difiering from that of said vehicle toimpart light-diffusing properties to the coating, the thickness of thecoating being proportioned with respect to the ratio of dye to vehicleand carrier solids so that the concentration of dye per squarecentimeter of surface of the coating does not exceed .0005 gram.

9. An article comprising a structure having a daylight fluorescentsurface area, said area comprising a layer of coating comprising a dyeexhibiting daylight fluorescence when in dilute solution, solidtransparent polymerized thermo-set resin particles bound together in acontinuous film, said dye being dispersed in said resin in a solvatedstate and retaining its daylight fluorescence when solvated in saidresin, the proportion of dye to resin being less than .01 gram per cubiccentimeter of resin and the thickness of the coating being proportionedwith respect to the ratio of dye to the solids of said coating so thatthe amount of dye per square centimeter of surface of the coating willvary between .00003 and .00006 gram.

10. A daylight fluorescent coating composition comprising a dyeexhibiting daylight fluorescence when in dilute solution, solidparticles of a polymerized thermo-set resin carrier in which said dye isdispersed in a solvated state and said dye retains its daylightfluorescence when solvated in said carrier, the maximum ratio of dye tocarrier being proportional to the wave-length of the dominantwave-length of light projected by the solvated dye and varying from amaximum of substantially .025 gram for dyes projecting yellow-greenlight to a maximum of substantially .015 gram for dyes projecting redlight per cubic centimeter of carrier, and a transparent liquidfilm-forming coating composition vehicle in which said carrier particlesare dispersed.

11. A daylight fluorescent coating composition comprising at least onedye exhibiting daylight fluorescence when in dilute solution, solidpigment particles comprised of a polymerized solvating thermo-set resincarrier for said dye, said dye being solvated in said carrier, themaximum concentrations varying according to the wave-length of thedominant wave-length of the light projected by said dye in theproportions of a maximum of substantially .025 gram for dyes projectingyellow-green light to a maximum of substantially .015 gram for dyesprojecting red light per cubic centimeter of solvating carrier and saiddye retaining its daylight fluorescence when solvated in said carrier,and a liquid transparent film-forming coating composition vehicle inwhich said pigment particles are dispersed, the maximum difference inindices of refraction of said carrier and vehicle being substantiallyfifteen percent of the larger index.

12. A daylight fluorescent coating composition as defined in claim 11 inwhich said carrier is pulverized, unplasticized polymerized resin of theclass consisting of unmodified urea-formaldehyde and butylalcohol-modified urea-formaldehyde.

13. A daylight fluorescent pigment consisting essentially of a dyeexhibiting daylight fluorescence when in dilute solution and apulverized, transparent polymerized thermo-set resin carrier solid inwhich said dye is solvated, the maximum ratio of dye to carrier varyingaccording to the wavelength of the dominant wave-length of lightprojected by s id solvated dye in the proportion of a maximum fsubstantially .025 gram for dyes projecting yellow-green light to amaximum of substantially .015 gram for dyes projecting red light percubic centimeter of solvating carrier and said dye' retaining itsdaylight fluorescence when solvated in said carrier.

14. A pigment as defined in claim 13 in which the proportion of dye tosolvating carrier is less than .01 gram of dye per cubic centimeter ofsolvating carrier.

15. A pigment as defined in claim 13 in which the solvating carrier isan unplasticized polymerized resin of the class consisting of unmodifiedurea-formaldehyde and butyl alcohol-modified urea-formaldehyde.

16. A display-comprising a support, a daylight fluorescent coatingcovering at least a delineated portion of the surface of said support,said coating comprising a dye exhibiting daylight fluorescence when saiddye is in dilute solution, solid particles of a transparent polymerizedthermoset resin carrier for said dye dispersed in said layer, saidcarrier maintaining said dye in a solvated state and said dye retainingits daylight fluorescence when solvated in said carrier, the maximumweight of said dye per volume of carrier varying from substantially .025gram for dyes projecting yellow-green light to substantially .015 gramof dye per cubic centimeter of solvating carrier for dyes projecting redlight and the weight of dye per square centimeter of surface of thearticle not exceeding .0005 gram of dye for each spectral waveband oflight projected and a transparent resinous vehicle binding said carrierparticles toether.

17. A display as claimed in claim 16 wherein the proportion of dye tocarrier is less than .01 gram of dye per cubic centimeter of compositionand the amount of dye per square centimeter of surface covered variesfrom .00006 and .00003 gram.

18. A display as claimed in claim 16 wherein the amount of dye persquare centimeter of surface covered is at least .000015 gram.

19. A display as claimed in claim 16 wherein the thickness of thecomposition on said support is such as to provide between .00015 and.00006 gram of solvated dye per square centimeter of surface covered bythe composition.

20. A display as defined in claim 16, in which the maximum difierence inindices of said resin 1B the support comprises paper.

. l7 18 24. A display as claimed in claim 16 wherein Number Name Datethe mpflses fabm- 2,084,526 Grenier June 22, 193': JOSEPH 2,113,090McKeag Apr. 5, 1938 ROBERT SWIT 5 2,149,993 Fonda Mar. 7, 1939 2,152,856Switzer Apr. 4, 1939 REFERENCES CITED 2,333,329 Migcarese' Nov. 2, 1948The following references are of record in the 2,341,009 Axelrad Feb. 8,1944 file of this patent: 2,360,516 Schmidling Oct. 17, 1944 UNITEDSTATES PATENTS 10 OTHER REFERENCES Number Name Date DeMent,"Flourochemistry," pp. 89-91, Chemi- 1,150,118 Hewitt A118- '1. 1915 calPublishing Co., N. Y. (1945) 2,037,793 Jacobson Apr. 21, 1936

13. A DAYLIGHT FLUORESCENT PIGMENT CONSISTING ESSENTIALLY OF A DYEEXHIBITING DAYLIGHT FLUORESCENCE WHEN IN DILUTE SOLUTION AND APULVERIZED, TRANSPARENT POLYMERIZED THERMO-SET RESIN CARRIER SOLID INWHICH SAID DYE IS SOLVATED, THE MAXIMUM RATIO OF DYE TO CARRIER VARYINGACCORDING TO THE WAVELENGTH OF THE DOMINANT WAVE-LENGTH OF LIGHTPROJECTED BY SAID SOLVATED DYE IN THE PROPORTION OF A MAXIMUM OFSUBSTANTIALLY .025 GRAM FOR DYES PROJECTING YELLOW-GREEN LIGHT TO AMAXIMUM OF SUBSTANTIALLY .015 GRAM FOR DYES PROJECTING RED LIGHT PERCUBIC CENTIMETER OF SOLVATING CARRIER AND SAID DYE RETAINING ITSDAYLIGHT FLUORESCENCE WHEN SOLVATED IN SAID CARRIER.